62 



EOCK-BOEEES. 



said to illuminate the mouth of the person who eats the 

 moUusk; and it is remarked by Dr. Priestly, that * 'contrary 

 to the nature of most fish, which give light when they tend 

 to putrescence, this is more luminous the fresher it is, and 

 when dried its light will revive on being moistened with 

 water." So that in more respects than one these rock-borers 

 are mysteries. The most common of them, perhaps, is the 

 Prickly Pidduck, or Peckstone, (P. dactylus,) which is much 

 used by the fishermen of our coasts as bait; the specific name 

 is the Latin for a fruit shaped like a finger, which is some- 

 thing like the shape of this mollusk, as will be seen by the 

 annexed engraving. 



The genus Pholus is very widely distributed, and all the 

 species have the same boring habits as those of our own 

 coast, which we need not enumerate. Like them too in 

 this respect are the marine worms called Teredo, which make 

 their way into the bottoms of ships, and all submerged tim- 

 ber, but these will be more fully spoken of in another volume. 

 The above figure exhibits the Pholas dactylus as it appears 

 in a section of rock, split open for the purpose of seeing the 

 shelly miner at his work. 



